An MRAM (Magnetoresistive Random Access Memory) can be rewritten at high speed compared to other nonvolatile memories. Thus, it is considered that the MRAM is applied to a working memory such as a main memory and a cache memory. When an MTJ element as a storage element of the MRAM is enabled to be accessed at high speed in order to apply the MRAM to a cache memory. It is likely that data retention characteristics deteriorate and data retention time becomes short under high temperature conditions. It is possible to keep data retention characteristics by performing verify writing after accessing the MRAM to write data therein, but the data may possibly disappear when the access interval becomes longer than the data retention time.
In order to lengthen data retention time, nonvolatile memories including the MRAM are written with data frequently under high stress conditions of high voltage and long pulse. This leads to a problem that rewriting resistance deteriorates due to the increase in power consumption and stress on memory elements.